The conversion of ammonia to ammonium

Options

A. on the ribosomes of cyanobacteria
B. on the endoplasmic reticulum of green algae
C. spontaneously when ammonia is in water
D. on the dry surface of soil particles

Answer

### Step-by-Step Solution:

1. **Understanding the Process**: The conversion of ammonia (NH₃) to ammonium (NH₄⁺) is an important biochemical process that occurs in various organisms, particularly in nitrogen-fixing bacteria like cyanobacteria.

2. **Role of Cyanobacteria**: Cyanobacteria are capable of fixing atmospheric nitrogen (N₂) and converting it into ammonia (NH₃). This process is known as nitrogen fixation.

3. **Conversion to Ammonium**: Once ammonia is produced, it can react with water (H₂O) to form ammonium ions (NH₄⁺). This reaction can be represented as:
\[ NH₃ + H₂O \rightleftharpoons NH₄⁺ + OH⁻ \]
This indicates that ammonia can accept a proton (H⁺) from water, resulting in the formation of ammonium.

4. **Location of Conversion**: The conversion of ammonia to ammonium primarily occurs in the ribosomes of cyanobacteria during the process of nitrification. This is the correct location for this conversion.

5. **Elimination of Incorrect Options**:
- **Endoplasmic Reticulum of Green Algae**: This is incorrect as the conversion does not occur here.
- **Spontaneously in Water**: While ammonia can exist in water, the conversion to ammonium is not spontaneous in the absence of biological processes.
- **On Dry Surface of Soil Particles**: This is also incorrect as the conversion requires moisture.

6. **Conclusion**: Based on the above analysis, the correct answer is that the conversion of ammonia to ammonium occurs on the ribosome of cyanobacteria.

### Final Answer:
The conversion of ammonia to ammonium occurs on the ribosome of cyanobacteria.

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